Two computers, one monitor, zero fiddling – Alex Plescan

This post details a "zero fiddling" solution for switching between two computers on a single monitor by leveraging DDC commands and a monitor's built-in KVM. It resonates with many developers who juggle work laptops and personal desktops, seeking seamless transitions. The popularity stems from its clever automation of a common, irritating workflow problem, despite the high upfront cost of the monitor.

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First Seen

May 18, 5:00 PM

Last Seen

May 19, 3:00 AM

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The Lowdown

Alex Plescan addresses a common predicament for home office workers: efficiently switching between a work laptop (macOS) and a personal desktop (Linux) using the same monitor, keyboard, and mouse. His goal was a completely hands-off solution, avoiding manual button presses or cable swaps. He achieves this through a clever combination of hardware and software:

The core hardware is a high-end monitor (specifically the MSI MPG 321URX) that features built-in KVM functionality. This allows USB peripherals plugged into the monitor to automatically follow the active video input source.
The "zero fiddling" part is enabled by Display Data Channel (DDC) commands, which allow a computer to send instructions (like changing input source) directly to the monitor over the display cable.
For macOS, he uses m1ddc (a command-line utility for Apple Silicon machines) and binds the input-switching command to a keyboard shortcut via Hammerspoon.
For Linux (using KDE), he employs ddcutil to send the necessary DDC commands, configuring the same keyboard shortcut through KDE's built-in shortcut manager.
He notes that a "DisplayPort" input code in ddcutil sometimes corresponds to the USB-C input when operating in DisplayPort Alt Mode.
The author suggests that Windows users might achieve similar hotkey functionality using the monitor manufacturer's bundled software.

This setup sidesteps the need for a separate physical KVM switch, providing an integrated, software-controlled solution for a seamless multi-computer workflow.

The Gossip

KVMs, Cost, and Clarifications

Many commenters immediately point out that the "zero fiddling" solution still involves a KVM, albeit one built into an expensive monitor (around $900). There's debate about whether this is a true "KVM-less" solution and if the cost undermines the premise, with some feeling the article lacked novel insights beyond purchasing a high-end monitor. Others, however, appreciate the specific hotkey automation of a built-in KVM, finding that insight valuable and new.

DDC Discoveries and Delights

A significant portion of the discussion expresses surprise and enthusiasm for the practical application of Display Data Channel (DDC) commands. Many users were unaware of the ability to control monitor settings like input switching programmatically via DDC and see its potential for solving similar KVM-like challenges. Some share tips for discovering DDC codes or note its long-standing presence and underutilization.

Alternative Approaches & Anecdotes

Users share their own experiences and alternative solutions for managing multiple computers with shared peripherals. These include software-based KVMs like Synergy, manufacturer-specific display managers (e.g., Dell Display Manager), or simpler methods like using `xrandr` to disable displays. Some discuss the challenges of multi-monitor setups, particularly concerning Linux and Nvidia, and potential race conditions with automation.